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Newton's Second Law formula:
story, analogy and memory trick

The Newton's Second Law formula is F = m × a. The net force on an object equals its mass multiplied by its acceleration, so the same push speeds up a lighter object more than a heavier one.

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PhysicsClass 9Class 11JEENEET

The Newton's Second Law formula

F = m × a
  • Fnet force, in newtons
  • mmass, in kilograms
  • aacceleration, in m/s²

The story

At a railway station, two friends give the same push to two trolleys. The empty trolley shoots ahead because its mass is small. The one stacked with luggage barely moves. The force F is the same, the mass m is different, so the acceleration a is different. To move the heavy trolley as fast, they need a bigger push.

Real-life analogy

Pushing an empty auto-rickshaw is very different from pushing a fully loaded one. With the same push, the loaded one picks up speed far more slowly.

Memory trick

Picture the loaded trolley: for the same F, a bigger m means a smaller a. Then rearrange the formula to a = F ÷ m.

Exam tip

F is the net (resultant) force, not just one of the forces. The unit is the newton, where 1 N = 1 kg·m/s². If the net force is zero, the acceleration is zero.

FAQ

Questions about Newton's Second Law

What is the Newton's Second Law formula?
F = m × a. The net force on an object equals its mass multiplied by its acceleration, so the same push speeds up a lighter object more than a heavier one.
How do I remember the Newton's Second Law formula?
Picture the loaded trolley: for the same F, a bigger m means a smaller a. Then rearrange the formula to a = F ÷ m.
What should I watch out for in exams with Newton's Second Law?
F is the net (resultant) force, not just one of the forces. The unit is the newton, where 1 N = 1 kg·m/s². If the net force is zero, the acceleration is zero.

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V = I × R

The current through a conductor is directly proportional to the voltage across it, as long as its resistance and temperature stay constant.

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Kinetic Energy

KE = ½ × m × v²

The kinetic energy of a moving object is half its mass times the square of its speed, so speed matters far more than mass.

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First Equation of Motion

v = u + at

The final velocity equals the initial velocity plus the acceleration multiplied by the time, for straight-line motion with constant acceleration.

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